Antenna feed point crossover



July 19, I966 J. c. HOLLOWAY ANTENNA FEED POINT CROSSOVER 2 Sheets-Sheet 1 Filed May 6, 1963 I'llllllll-Il T POWER SOURCE FOR LIGHT I SIGNAL POWER OUTPUT FROM TRANSMITTER INVENTOR.

Jesse C. Holloway COAXIAL SIGNAL. INPUT POWER SOURCE FOR LIGHT Agents July 19, 1966 J. c. HOLLOWAY ANTENNA FEED POINT CROSSOVER 2 Sheets-Sheet 2 Filed May 6, 1963 F'eEB 'ssmT CROSSOVER INVENTOR. Jesse C Holloway Agenfs United States Patent Iowa Filed May 6, 1963, Ser. No. 278,347 4 Claims. (Cl. 343-859) This invention pertains to multiple antenna feeders and particularly to high-frequency antenna feed point crossovers operable over a wide range of frequencies.

Often an aircraft obstruction light, or another antenna, or both are to be placed on an antenna structure above a wide-frequency antenna. The usual methods of employing quarter-wave stubs that are effective to provide high impedance over a narrow frequency range are not applicable to provide a connection through the field of the widefrequency antenna. Any conductor through the field becomes resonant at certain frequencies within the wide-frequency range and functions as a reflector to distort the field pattern of the antenna. When the wide-frequency antenna is fed by a coaxial cable, one or more other cables for feeding power loads, such as other antennas or obstruction lights, may be shielded from the field of the antenna by being run within a hollow inner conductor of the coaxial cable.

Through the use of the feed point crossover of this invention, auxiliary cables for supplying power to loads mounted above a wide-range antenna may be introduced into a duct within the inner conductor of a coaxial feeder without disturbing the transmission characteristics of the feeder. The feed point crossover described in detail below comprises two sections of coaxial conductors connected as a balun; the balun is equivalent to two baluns of the type for connecting a coaxial cable to an open line, the open line portions being connected together to provide coaxial connections at both input and output; the center conductor of at least one of the sections is hollow to form a duct for introducing auxiliary cables; and the auxiliary cables are run from a power source through the duct of one of the center conductors for connection to cables within the center conductor of the antenna feeder.

An object of this invention is to provide a crossover point for introducing auxiliary cables into the center conductor of a coaxial cable that functions over a high-[frequency range.

Another object is to provide a feed point crossover that may be used in high power antenna installations.

The following description and the appended claims may be more readily understood by reference to the accompanying drawings in which:

FIG. 1 is a bialun type [feed point crossover that functions over a moderate frequency range;

FIG. 2 is a balun type feed point crossover that function-s over a very wide frequency range;

BIG. 3 is a sectional view taken along line 33 of FIG. 1 which more clearly shows the construction of the invention;

FIG. 4 is a view taken along line 4-4 of FIG. 2;

FIG. 5 shows the application of the antenna feed point crossover of this invention to a discone antenna installation;

FIG. 6 is a view taken along line 66 of FIG. 5.

Antenna feed point crossover 11 of FIG. 5 is shown applied to a discone antenna installation 12. An incoming coaxial power cable 13 [from a remote transmitter is connected through the feed point crossover 11 to the coaxial feed cable that comprises the outer conductor 14- and the hollow inner conductor 15. The outer conductor 14 is usually a ground connection and is connected to the cone of the antenna 12; the inner conductor 15 is connected to the horizontal disk of the antenna. The coaxial cable is located within a central hollow supporting mast 16. An auxiliary power cable 17 is connected from a source of power to a top aircraft obstruction light 18. At the feed point crossover 11, the cable 17 enters a duct within the inner conduct-or 15 of the antenna feed cable. The construction of the feed point crossover 11 provides a point at ground potential for the auxiliary cable to enter the hollow inner conductor 15 so that the transmission characteristics of the antenna feed cable are not disturbed by undesired reflections. The coaxial relationship of conductors 14, 15, and 16 and cable 17 is more clearly drawn in FIG. 6.

In FIG. 1, the feed point crossover comprises two sections 19 and 20 of coaxial conductors connected to form two complete circuits, each circuit comprising an outer.

conductor of one section and an inner conductor of the other section. One circuit may be traced from ground 33 at the input of the crossover 11, through the outer conductor 21 of section 19, the interconnection 22 between the output ends of the sections, the inner conductor 23 of the section 20 back to ground 34 at the input end. A similar circuit starting at the output end may be traced from ground 35, through the outer conductor 24 of section 20, interconnector 25, inner conductor 26 of section 19 to ground 36. The crossover point corresponds to two conventional baluns. If each of the sections 19 and 20 were cut across the conductors into two equal end portions, the outer conductors of each end portion where they were cut apart could be grounded and the inner conductors of each end portion at the same point could be connected to a balanced line. By continuing the coaxial lines as shown for sections 19 and 20, obviously the input and the output of the crossover point assembly are each suitable for connection to a coaxial line. By having the inner conductor of at least one of the sections hollow to provide a duct, any required auxiliary line may be introduced into the hollow inner conductor of the coaxial section at a point that is connected to ground.

The coaxial power cable from a transmitter is connected to that end of coaxial line section 19 that has its outer conductor 21 connected to ground 33 and its inner conductor connected to the ungrounded adjacent end of the outer conductor 24 of section 20. The coaxial antenna feed line comprising outer conductor 14 and hollow inner conductor 15 is connected to the output end of section 20 so that a continuous shielded duct is formed through the inner conductor 23 of section 20 and the inner conductor 15. The power cable 17 for supplying power to the obstruction light 18 is introduced into the duct of inner conductor 23 at the point at which it is grounded.

The coaxial conductor sections of the feed point crossover 11 function according to usual balun principles. The phase of signal at any point on the line sections is dependent upon the inductance and transit time of the conductors. At the lower frequency limits of the feed point crossover of FIG. 1, the signal tends to become short circuited because of the decreased inductance of the two circuits that are within the crossover as traced above. The sections are coiled as in FIG. 1 to increase the inductance of each circuit so that the range of frequencies for satisfactory operation is extended to lower limits as compared with the lower frequency limits of straight sections that have the same lengths of coaxial conductors. This system with coiled conductors operates with little power loss over a frequency range of about 3/1 ratio and may operate quite satisfactorily over a frequency range of 4/1.

0 For a very high ratio of frequencies, a feed point crossover that uses wide band tapered baluns as shown in FIG. 2 is recommended. Theoretically, the range of frequencies of the tapered baluns is limited only by the precision with which they may be fabricated and by the losses caused by radiation from the tapered edges at very high frequencies.

The feed point crossover of FIG. 2 is similar to that shown in FIG. 1 in that the terminals of two balun sections that are commonly connected to open balanced lines are connected directly together. The terminal that corresponds to an outer conductor of each section, and that is usually connected to an open line, is connected to the terminal of the other section that corresponds to the inner conductor that is usually connected to an open line. Each section of the feed point crossover of FIG. 2 is a wide band tapered balun as described in United States Patent 3,013,226 issued to R. H. Du Hamel, et al. on December 12, 1961, and therefore the physical construction of this embodiment can be understood by making reference to said patent. FIGURE 4 shows the tapered construction of a single balun. The embodiment of FIG. 2 is actually two such baluns placed end-to-end with the inner and outer conductors electrically and mechanically contiguous. A balun of this type operates satisfactorily over a frequency range of 100/1 or greater. A transitional slit started in the outer coaxial conductor near one end of the tapered balun is gradually opened until the center conductor and the remnant of the outer conductor provide an open transmission line. As described in United States Patent 3,013,226, the slit is formed by removing progressively material from the outer conductor so that the characteristic impedance of the balun transformer follows a Tohebycheff response in the pass band over which the balun is to be utilized. The outer conductor 27 at the input of one section of the crossover has a tapered portion 2 8 that decreases the area of the outer conductor so that it becomes a conductor parallel to the extension of inner conductor 29. The outer conductor 27 is then continued by the hollow conductor 30 that becomes the center conductor of the coaxial output. In a similar manner, the. outer conductor 31 of the output of the crossover has a tapered portion 32 that is decreased in cross section and connected to the inner conductor 29 of the coaxial input. The coaxial signal input 13 from a transmitter is connected to the outer conductor 27 and the inner conductor 29, and the coaxial antenna feed having outer conductor 14 and an inner conductor 15 is connected to outer conductor 31 and the inner conductor 30 at the output of the feed point crossover. The hollow inner conductor 30 is connected with the inner conductor 15 to provide a duct for the auxiliary power cable 17 that is connected to the obstruction light 18. The cable 17 is introduced at the grounded point of the conductor 30 at the input of the feed point crossover.

Although this invention has been described with respect to particular embodiments thereof, it is not to be so limited, as changes and modifications may be made therein which are within the spirit and scope of the invention as defined by the appended claims.

What is claimed is:

1. A high-frequency feed point crossover comprising, a balun transformer having first and second coaxial terminals, each terminal having an inner and an outer conductor, the outer conductors of each terminal being at common reference ground potential, balun transformer means for gradually transforming impedance between said first and second coaxial terminals so that the impedance of the outer conductor of said first terminal is gradually increased with reference to ground as the second of said terminals is approached and the impedance of the outer conductor of said second terminal is gradually increased with reference to ground as the first of said terminals is approached, the outer conductor of said first terminal being connected to the inner conductor of said second terminal at one end of said terminals, the outer conductor of said second terminal being connected to the inner conductor of said first terminal at the other end of said terminals, the inner conductor of at least one of said terminals being hollow to form a shielded duct, and an auxiliary power line running through said duct.

2. In an antenna installation having an antenna and an auxiliary feed line passing through the field of said antenna, an antenna feed cable connected to said antenna, said antenna feed cable having an outer conductor and a coaxial inner conductor, said inner conductor being hollow to provide an inner shielded duct, said auxiliary feed cable running within said duct of said inner conductor to shield said auxiliary feed cable while it passes through the field of said antenna, a power cable for supplying highfrequency power to said antenna; a feed point crossover, said feed point crossover having an input coaxial section and an output coaxial section, each of said coaxial sections having an inner and an outer conductor, said power cable being connected to said input coaxial section, said antenna feed cable having its outer and inner conductors connected to the outer and inner conductors respectively of said output coaxial section, the inner conductor of said output coaxial section being hollow to extend said shielded duct through said output coaxial section, the outer conductor of said input coaxial section being connected to the inner conductor of said output coaxial section, the outer conductor of the output coaxial section being connected to the inner conductor of the input coaxial section, lbalun transformer means between said input and output sections to cause the impedance of the outer conductor of each of said sections to be increased gradually with reference to a common reference ground as the other of said sections is approached, and said auxiliary feed line extending through said shielded duct of said antenna feed cable and said output coaxial section of said feed point crossover.

3. An antenna installation according to claim 2 in which said input and said output coaxial sections are required lengths of coaxial cable to provide change of impedance over a desired frequency range of power to be supplied to said antenna, the outer conductor of said coaxial input section being connected to ground at the end to which said power cable is connected, and the inner conductor of said coaxial input section being connected to ground at the other end, said hollow inner conductor of said coaxial output section being connected to ground at the end opposite said antenna feed cable, the outer conductor of said coaxial output section being connected to ground at the end which is connected to said antenna feed cable.

4. The antenna installation of claim 2 wherein the connections of said inner and outer conductors are effected by a mechanically contiguous and electrically conductive relationship of said input and output coaxial sections.

References Cited by the Examiner UNITED STATES PATENTS 2,102,410 12/1937 Fyler 343721 2,140,174 12/1938 Smith 34372l 2,692,335 10/1954 Alford 343704 X 2,925,566 2/1960 Jasik 33326 3,013,226 12/1961 Du Hamel et a1 33326 3,217,274 11/1965 Alford 343821 X FOREIGN PATENTS 811,351 4/1959 Great Britain.

HERMA-N KARL SAALBACH, Primary Examiner.

P. L. GENSLER, Assistant Examiner. 

1. A HIGH-FREQUENCY FEED POINT CROSSOVER COMPRISING, A BALUN TRANSFORMER HAVING FIRST AND SECOND COAXIAL TERMINALS, EACH TERMINAL HAVING AN INNER AND AN OUTER CONDUCTOR, THE OUTER CONDUCTORS OF EACH TERMINAL BEING AT COMMON REFERENCE GROUND POTENTIAL, BALUN TRANSFORMER MEANS FOR GRADUALLY TRANSFORMING IMPEDANCE BETWEEN SAID FIRST AND SECOND COAXIAL TERMINALS SO THAT THE IMPEDANCE OF THE OUTER CONDUCTOR OF SAID FIRST TERMINAL IS GRADUALLY INCREASED WITH REFERENCE TO GROUND AS THE SECOND OF SAID TERMINALS IN APPROACHED AND THE IMPEDANCE OF THE OUTER CONDUCTOR OF SAID SECOND TERMINAL IS GRADUALLY INCREASED WITH REFERENCE OF GROUND AS THE FIRST OF SAID TERMINALS IS 